drm/amdgpu: Fix a false positive when pin non-VRAM memory

Flag TTM_PL_FLAG_CONTIGUOUS is only valid for VRAM domain. So fix the
false positive by checking memory type too.

Suggested-by: Felix Kuehling <Felix.Kuehling@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: xinhui pan <xinhui.pan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>